Work has continued on problems related to the viability and oxygen-tranport function of red blood cells using 1) mature erythrocytes from man and a number of domesticated and wild mammals, 2) reticulocytes from rat, rabbit and pig and 3) red cells from embryos, at different stages of development, of several birds (chicken, duck, pigeon and gull) and reptiles (alligator, iguana, rat snake and land and sea turtles).